In recent years, global scale environmental destruction problems such as global warming, ozone layer depletion, acid rain, etc. have gained prominent attention. Internationally, environmental pollution measures are advocated, and various regulations have been established from the viewpoint of environmental protection. Among them, release into the atmosphere of organic solvents (VOC) has been a serious problem, and also in each industry, the movement for de-organic solvents (de-VOC) along with the trend for strengthening VOC regulations has become active. Also in the paint industry, as a substitute for conventional organic solvent-based coating material, a powder coating material is highly expected as a coating material which contains no VOC and which is friendly to the environment as it can be recovered and reused without requiring exhaust treatment or wastewater treatment.
As such a powder coating material, an acrylic resin powder coating material, a polyester resin powder coating material or an epoxy resin powder coating material, is mainly used. However, coating films formed by using these powder coating materials have such a drawback that they are poor in weather resistance.
As a powder coating material which is excellent in weather resistance, a fluororesin-type powder coating material using a fluororesin has also been developed.
As the fluororesin-type powder coating material, for example, the following powder coating material has been proposed.
(1) A powder coating material obtained by dry blending a powder of a vinylidene fluoride copolymer having a melting point of at most 150° C., a crystallinity of at most 35% and a mass average molecular weight of from 1×104 to 5×105, and a powder of a methyl methacrylate copolymer having a glass transition temperature of at most 110° C. and a mass average molecular weight of from 1×104 to 5×105; or a powder coating material obtained by seed-polymerizing a monomer capable of forming the methyl methacrylate copolymer in an aqueous dispersion of the vinylidene fluoride copolymer, and spray drying the obtained aqueous dispersion (Patent Document 1).
As the methyl methacrylate copolymer in the powder coating material (1), a copolymer of methyl methacrylate and a monomer copolymerizable with methyl methacrylate such as n-butyl acrylate or t-butyl methacrylate may be used.